This invention relates to a foundry composition from which foundry moulds or cores are to be formed.
In U.S. Pat. No. 3,925,296 there is claimed a foundry binder composition comprising a polyisocycanate and a bisphenol. In the process disclosed in the patent, a foundry aggregate is mixed with a binder, formed to the required shape and the mixture is then cured by passing triethylamine through the shaped mixture. I have found that the strength of cores formed by this method and using a binder comprising a polyisocyanate and bisphenol-A decreases over a period following curing and that this decrease in strength is such as to make the method unsuitable for foundry use.
I have further discovered that this disadvantage can be reduced or overcome by modifying the binder composition used in the method.